Birds 'Pack Light' for Flying, Study Finds

December 22, 2008 - News Release

People taking part in the annual Christmas Bird Count might be interested in a new study by a University of Guelph biologist. Prof. Ryan Gregory found that when birds fly south for the winter, they tend to pack light for the trip — at least when it comes to their DNA. (This research was highlighted recently in the Globe and Mail - Read More).

Flying limits the amount of genetic baggage that an avian species can carry around, Gregory said. It's not that birds might be literally weighed down by dragging along too much DNA. Rather, it's that flight costs so much energy-wise that birds' cells — and the genetic material inside them — need to remain as trim as possible.

The most productive fliers are those with the lightest genome load, said Gregory, a professor in Guelph's Department of Integrative Biology who conducted the largest-ever study on the subject. His research was also the first to link birds' genome size with wing size to directly measure flight efficiency.

"You see some obvious differences between the emu and the hummingbird in terms of the amount of DNA," said Gregory.

His study, published in Proceedings of the Royal Society B, looked at songbird genomes and flight. Songbirds, make up the largest single group of birds, with about 5,700 species.

The researchers sampled birds caught and released at the Long Point Bird Observatory on Lake Erie. Besides weighing the birds and collecting blood samples, they looked at wing span and used wing area to calculate a wing loading index. That allowed them to compare flying efficiency or strength.

They found that stronger or more specialized flyers have smaller genomes. Among 18 families of songbirds in the study, tree creepers, chickadees and kinglets had the smallest genomes; finches, warblers and thrushes had the largest.

Flying takes a lot of energy, said Gregory. Smaller cells with relatively high surface areas allow for better exchange of oxygen and carbon dioxide during all that effort.

As a group, birds have the smallest and least variable amounts of DNA compared to amphibians, reptiles and mammals, and other research suggests their genomes first started shrinking pre-flight, back when dinosaurs still roamed the Earth.

For example, a study of dinosaur cells published in Nature last year found that theropod dinosaurs — the group that led to modern birds — had smaller genomes than other branches that were more like today's reptiles.

Higher metabolic rates in theropods may have driven genome size down initially, helping to set the stage for flight requirements when their feathered descendants lifted off, Gregory said. He conducted his study with master's student Chandler Andrews and U of G zoology grad Stuart Mackenzie, the program co-ordinator at the Long Point Bird Observatory.

Did You Know?
Every year, thousands of bird enthusiasts across North America take part in the Christmas Bird Count, considered to be the world's most significant citizen science-based conservation effort.

This year is the 109th annual event. More than 2,000 counts are scheduled to take place across the continent between Dec. 14 to Jan. 5, 2009, with more than 100 in Ontario alone. Last year, nearly 58,000 volunteers counted some 70 million birds.

The gathered data is used by groups such as Bird Studies Canada, the Canadian Wildlife Service and the National Audubon Society to monitor the status of all bird species in the western hemisphere.

The Christmas Bird Count was started more than 100 years ago by American ornithologist Frank Chapman. He proposed the count as an alternative to the then-popular "side hunt" in which teams competed to see who could shoot the most birds and small mammals as a Christmas day activity.

Want to learn more about the birds you might see in your backyard during winter?
U of G's Arboretum has put together a booklet, "Feeder Birds of the Arboretum," that covers winter birds. It contains more than 95 colour photos. Read more

For media questions, contact Communications and Public Affairs: Lori Bona Hunt, 519-824-4120, Ext. 53338/, or Barry Gunn, Ext. 56982/

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